This invention relates to a refrigeration apparatus for containers used for transporting perishable food.
Generally, perishables must be stored at optimum temperatures to maintain the freshness. For example, if the perishables to be stored are vegetables and fruits, a temperature range that is not too low is required. Likewise, fish and meat of which the taste deteriorates due to freezing needs to be stored at a temperature that does not cause freezing.
To meet such freshness requirements, perishables are usually transported by air which is shorter in time than other transportation means. When transporting perishables which deteriorate very quickly, it is very difficult to maintain the freshness of the commodities when using transportation means other than air transportation.
To overcome this difficulty with non-air transport systems, the idea of controlling the humidity, in addition to setting the temperature of the transport container has been used to maintain the freshness of the commodities to be transported. (i.e. A refrigeration container is provided with a humidifying apparatus for transporting perishables.) Since humidity as high as 85 to 95% is generally required in these containers, a humidifying apparatus and its peripheral equipments of higher performance are required.
A conventional humidifying apparatus installed in a container to meet this requirement is disclosed in Japanese Utility Model Application Laying Open Gazette No. 63-63671. The humidifying apparatus in this application consists mainly of an ultrasonic humidifier (a), reserve tanks (b), and a pump (c) (See FIG. 4). The ultrasonic humidifier is continuously fed with water by the pump (c) through a feed water pipe (d). Surplus water in the ultrasonic humidifier (a) continuously returns to each reserve tank (b) through a return pipe (e). The water in the ultrasonic humidifier (a) is atomized by the ultrasonic waves of a vibrating portion of the humidifier and is discharged.
Heaters (f) for preventing freezing of the water in the pipes are disposed respectively in the ultrasonic humidifier (a) and each reserve tank (b). Each reserve tank (b) is connected with a drain pipe (h) for returning water and residue collected in a drain pan (g) located at the lower part of the refrigeration unit. The drain pipe is drained by a plug. Water collected in the drain pan (g) is recycled.
Humidifying apparatus provided with heaters for preventing freezing of water in the pipes have disadvantages such as reduced maintainability and increased cost due to complex construction. These problems are caused by the following reasons.
(1) An electric heater having a limited life involves regular maintenance.
(2) Safety devices are necessary to avoid breakdown of the heater when water in the reserve tank is depleted.
(3) A thermostat is required for controlling the water temperature according to the amount and the temperature of water in the reserve tank and ultrasonic humidifier.